The present invention relates to a transmission for automobiles, and more particularly to a hydraulic transmission equipped with a lock-up clutch.
A fluid torque converter such as is now widely used for a hydraulic transmission for automobiles comprises an impeller connected to the engine output shaft, a turbine connected to the input shaft of a gear transmission mechanism, and a stator adapted to deflect the flow of fluid which returns from said turbine to said impeller in order to effect torque conversion between the engine output shaft and the input shaft of the gear transmission mechanism, according to the difference between the rotational speed of said output shaft and said input shaft, while transmitting rotational power. In this torque converter, there exists inevitably a slippage between the impeller and the turbine even under the optimum operating condition where the rotational speed of the turbine has almost approached the rotational speed of the impeller. This slippage lowers the power transmission efficiency as compared with that of direct power transmission by a mechanical clutch. This results in poor fuel consumption of the automobile, which leads to problems regarding economy of petroleum and quality of exhaust gas.
In order to solve these problems, a hydraulic transmission system equipped with a lock-up clutch has been proposed. This system includes in parallel a hydraulic transmission, as, for example, a torque converter, and a friction clutch, the latter being adapted to be selectively actuated for effecting direct transmission, according to the operational condition of the automobile.
Various types of hydraulic transmissions with lock-up clutches have been proposed, including a typical one disclosed in U.S. Pat. No. 3,338,358 and our former proposal set forth in U.S. Pat. No. 4,108,289. However, one problem concerned with these known types of hydraulic transmissions having lock-up clutches is that the axial length of the transmission becomes substantially longer than that of a corresponding hydraulic transmission having no lock-up clutch, due to the fact that the lock-up clutch is contained in a transmission housing which encloses a turbine and stator in its front portion and provides an impeller by its rear portion. The lock-up clutch is positioned between the front end wall of the housing and the turbine and generally includes a piston or diaphragm which operates as a hydraulic actuator for the lock-up clutch and a clutch disk, axially arranged in sequence. In particular, when a buffering means is incorporated in the clutch disk so as to lessen the shock caused at the engagement and disengagement of the lock-up clutch, the axial space required for mounting the clutch disk becomes substantially large, because such a buffering means generally includes one or two auxiliary disk members arranged axially in sequence and several coil springs incorporated in the assembly of the clutch disk and the auxiliary disk members along the peripheral portions of the auxiliary disk members. However, in the design of automobiles, it is often very important that the axial dimension of the hydraulic transmission should be limited without a certain relatively small axial length, and in view of this it is strongly desirable for a lock-up clutch to be incorporated in a hydraulic transmission without substantially increasing the overall axial length of the transmission.